The tutorial of the O.P is obsolete.
In both cases, remove security from the lock screen and restart the system before starting.
Old rom in Fastboot.ZIP
)then updated via Ota and Twrp.
Install the Twrp and flash the last rom in ZIP
Reboot the phone to fastboot (Power + Vol Down)
Connect the phone to the computer using an USB cable (Preferred to use original cable that came with the phone)
Extract the fastboot files and open CMD/Terminal there.
Paste the twrp.img in the same folder.
Type' fastboot boot twrp.img' .
The phone will reboot in TWRP after that go to Advanced > Flash Current TWRP.
Twrp/wipe/format data type yes
If errors,red lignes,restart the procedure.
Put the rom in internal storage or use OTG
First boot takes time 5/8 minutes.